The present invention relates to a liquid filter, in particular for oil or fuel in an internal combustion engine, and a suitable engine-side filter connection flange.
A first liquid filter and a suitable filter connection flange are known from DE-U 94 11 212. In this case the liquid filter comprises a front-side circular groove at the front wall facing the filter connection flange with an axial sealing ring inserted in the groove. With this front wall, the liquid filter is pressed at a corresponding sealing surface of the filter connection flange. In this filter the pressing force is exerted by a hollow fastening screw bolt arranged in the interior of the filter housing with the screw bolt screwed together with a connection piece with an outer thread forming a part of the filter connection flange.
It is a disadvantage of this known liquid filter that the filter housing at least in the area of the front wall thereof is relatively rigid and thereby heavy in order to guarantee the necessary power transfer from the center screw bolt to the radially outwards positioned sealing without distortion or damage to the filter housing over a long period of time. This power transfer is necessary for the axial sealing. When selecting the material for the filter housing, one is restricted to metals, because plastic materials are not able to handle with the necessary stresses. Furthermore, the mounting of the known liquid filter on the engine-side filter connection flange is relatively cumbersome because the fastening screw bolt is positioned deeply in the interior of the filter housing and thus the handling with a wrench or tool is difficult.
Additionally from the DE 34 44 267 A1 a liquid filter with a housing receiving a filter insert is known, with the housing comprising a base member or socket with an inlet and drain for liquid to be filtered and wherein the socket is designed as a heat exchanger. Beside passages for the liquid to be filtered with a drain duct centrally arranged in the base member and extending across the total height thereof the socket comprises also adjacent further ducts for the heat exchanger fluid. Therein the liquid to be filtered is guided in an annular duct area within the socket concentric with the drain duct. Two further concentric annular ducts are arranged on both sides of the annular duct area. The base member or socket consists of two members sealed against each other and inserted into each other wherein the sealing is attained by several concentric radial seals. Regarding the mounting of the liquid filter at an associated engine, e.g. the internal combustion engine of a passenger car, a flat filter connection flange is provided at the engine-side and a mirror symmetric connection flange of the filter housing is to be biased against the flat filter connection flange with a flat axial sealing inbetween.
Also with this known liquid filter there is the requirement that the filter housing in the area of the connection flange has to comprise a high strength in order to guarantee a continuous seal of the flange connection during operation. All materials having the tendency to deform under the influence of temperature and pressure therefore disadvantageously cannot be used in this known liquid filter for the housing thereof in particular for the base member or socket.
From the DE 36 25 764 C1 a lube oil filter for internal combustion engines with a replaceable filter insert is known. In this filter the filter housing receiving the filter element is formed as a disposable unit which is firmly connected with the housing main member containing the inlet and drain ducts by means of a center screw bolt extending through the disposable unit. In order to guarantee a replacement of the seals when replacing the filter element the disposable unit is formed such that the seals have to be removed when removing the displaceable unit. The housing main member is formed with an outer cup-shaped circumferential wall and with a concentric inner pipe-like connection piece wherein the filter housing with the front end thereof is inserted into the annular space between the circumferential wall and the pipe-shaped connection piece. Therefore at the outside of the filter housing a radial sealing is provided; at the inner side of the filter housing a combined axial and radial sealing is attached. Regarding the fastening of the housing main member at the internal combustion engine only a flat flange connection is disclosed which is visible in the single figure of the drawing in the lower left corner. Therefore in this known liquid filter the connection with the engine block of the associated internal combustion engine is to be attained by an inbetween flat sealing which has to be axially biased.
For guaranteeing the seal of the flange connection between the filter housing and the internal combustion engine during operation over a sufficiently long period of time the material of the housing main member of the filter has to be sufficiently stable which excludes the use of plastic material.